1. Field of the Invention
The present invention relates to an image printer and, more particularly, to an image printer in which a multi-color toner image is formed on a printing body.
2. Description of the Prior Art
As a method printing with a plurality of colors using an image printer utilizing electrophotographic method such as a copying machine, a laser printer or the like, there is known a method where by providing a plurality of developing units containing different color toners, a first color image is formed on a printing body by performing a first charging process, a first exposing process and a first developing process to the printing body, and successively a second color image is formed on the printing body by performing a second charging process, a second exposing process and a second developing process to the printing body, and then the first color and the second color toner images are transferred onto a print material such as a sheet of paper at a time.
In a case of forming the second color toner image onto the printing body on which the first color toner image exists, there arises a problem in that the first color toner image is disturbed by a magnetic brush of the developing unit for the second color when the printing body passes by the developing unit for the second color, the scraped toner enters into the developing unit for the second color and is finally mixed with the second color toner to print an image having a color tone different from its original.
In a case of using a two-component developing agent composed of a toner and a carrier as the developing agent, there are deviations in the particle size and the magnetic characteristic (saturation magnetization) of a carrier used, and a carrier having a small particle size or a small saturation magnetization is apt to be attached onto a printing body since such a carrier is held with a small force by the developed magnetic pole. Once the carrier is attached onto the printing body, the carrier interrupts supplying of toner to an electrostatic latent image formed formed thereon. As a result, this causes omitted letters and accordingly degrades the printing quality.